Apparatus and method for fabricating high strength long nanostructured tubes

Abstract

An improved apparatus and method of fabricating long nanostructured or ultrafine grained tubes includes, in one implementation, expanding and extruding a sample material through cyclic deformations. The first cycle begins with expanding the sample through a die unit by applying pressure using a punch box, then with extruding the sample by applying back pressure using a stationary mandrel, which in turn reduces the expanded sample diameter to the original diameter. The next cycle begins with inverting the die unit to further extrude the sample with no need to apply back pressure. Furthermore, resistant forces against the sample are reduced by using a lubricant material inside the die unit, thus allowing continuation of additional cycles without constraining the sample length, resulting in desired strength and elongation.

What is claimed is: 
     
       1. An apparatus for fabricating a nanostructured tube from a sample billet, comprising:
 a moving mandrel; 
 wherein the moving mandrel is configured to be positioned inside the sample billet such that the moving mandrel simultaneously moves with the sample billet, the moving mandrel extending between a first end of the sample billet and a second end of the sample billet; 
 a holder unit; 
 a die unit having a top end, a bottom end, and a plurality of grooves, the die unit secured to the holder unit, and the die unit configured to extrude the sample billet through the plurality of grooves to increase a diameter of the sample billet; 
 an inlet channel having a first end and a second end, the first end configured to load the sample billet, and the second end connected to the top end of the die unit; 
 a punch box having a top end and a bottom end, the bottom end of the punch box in contact with the first end of the inlet channel, the punch box configured to push the sample billet forward through the die unit and to seal the inlet channel; 
 a lubricant material inside the die unit is configured to fill a space gap between the sample billet and the die unit, and to avoid a direct contact between the sample billet and the die unit; and 
 a stationary mandrel having a first end and a second end, the first end of the stationary mandrel in contact with the sample billet, the second end of the stationary mandrel extending to the bottom end of the die unit, the stationary mandrel configured to apply back pressure to the sample billet; 
 wherein:
 the stationary mandrel is arranged to apply back pressure to the sample billet to reduce the increased diameter of the sample billet during an initial extrusion cycle, 
 the stationary mandrel is arranged to be removed after the initial extrusion cycle, and 
 the die unit is arranged to be inverted after the initial extrusion cycle in order for the punch box to further extrude the sample billet through the plurality of grooves, and to further reduce the increased diameter of the sample billet. 
 
 
     
     
       2. The apparatus of  claim 1 , wherein the moving and stationary mandrels have cylindrical shapes and are made of solid materials. 
     
     
       3. The apparatus of  claim 1 , wherein the die unit has a cylindrical shape, and a cross-section of the die unit includes a central opening and a plurality of peripheral openings in which the central opening is configured to allow loading of the sample billet through the die unit, and the plurality of peripheral openings are configured to control a shrinkage and flow characteristic of the sample billet during extrusion. 
     
     
       4. The apparatus of  claim 1 , wherein each one of the plurality of grooves inside the die unit includes an expanded section with a larger diameter than other sections of the groove to increase the diameter of the sample billet during extrusion. 
     
     
       5. The apparatus of  claim 1 , wherein a position of the moving mandrel inside the sample billet reduces a relative velocity between the sample billet and the moving mandrel to reduce a resistance force against the sample billet during extrusion. 
     
     
       6. The apparatus of  claim 5 , wherein the lubricant material prevents friction between the sample billet and the die unit to reduce an amount of the resistance force against the sample billet during extrusion. 
     
     
       7. The apparatus of  claim 6 , wherein the lubricant material applies a hydrostatic pressure to the sample billet to reduce an amount of force required for the punch box to push the sample billet forward through the die unit during extrusion. 
     
     
       8. The apparatus of  claim 7 , wherein reduction in the amount of force required allows continuation of additional cycles of extrusion without a need to constrain a sample length. 
     
     
       9. The apparatus of  claim 1 , wherein during an extrusion cycle at least one of the stationary mandrel or the punch box applies an amount of strain on the sample billet, and the amount of strain deforms the sample billet to generate an ultrafine grained nanostructure for the sample billet. 
     
     
       10. The apparatus of  claim 9 , wherein a total amount of strain applied on the sample billet is equal to a summation of each of the amount of strain applied in each of the extrusion cycles. 
     
     
       11. The apparatus of  claim 9 , wherein the ultrafine grained nanostructure increases a mechanical strength of the sample billet. 
     
     
       12. A method of fabricating a nanostructured tube comprising:
 placing a moving mandrel inside a sample billet; 
 loading the sample billet into an inlet channel of an extrusion machine, the extrusion machine including a punch box, a die unit and a stationary mandrel, a top end of the die unit in contact with one end of the punch box and a bottom end of the die unit extended to one end of the stationary mandrel; 
 pouring an amount of a lubricant material inside the die unit to fill a space gap between the sample billet and the die unit, and to avoid a direct contact between the sample billet and the die unit; 
 applying pressure by the punch box to push the sample billet forward through a plurality of grooves inside the die unit to increase a diameter of the sample billet and to seal the inlet channel; 
 applying back pressure by the stationary mandrel to extrude the sample billet through the plurality of grooves inside the die unit; 
 removing the stationary mandrel; 
 inverting the die unit; 
 upon removing the stationary mandrel and inverting the die unit, applying further pressure by the punch box to further extrude the sample billet through the plurality of grooves to reduce the increased diameter of the sample billet; and 
 repeating steps of inverting the die unit and applying further pressure by the punch box to further extrude the sample billet through the plurality of grooves a plurality of times. 
 
     
     
       13. The method of fabricating a nanostructured tube of  claim 12 , wherein a simultaneous movement of the sample billet and the moving mandrel zeros out a relative velocity between the sample billet and the moving mandrel to reduce a resistant force against the sample billet during extrusion. 
     
     
       14. The method of fabricating a nanostructured tube of  claim 12 , wherein the lubricant material prevents friction between the sample billet and the die unit to reduce a resistance force against the sample billet during extrusion. 
     
     
       15. The method of fabricating a nanostructured tube of  claim 12 , wherein extrusion through the plurality of grooves inside the die unit reduces the increased diameter of the sample billet to an original diameter of the sample billet. 
     
     
       16. The method of fabricating a nanostructured tube of  claim 12 , wherein the lubricant material applies a hydrostatic pressure to the sample billet to reduce an amount of force required for the punch box to push the sample billet through the die unit during extrusion. 
     
     
       17. The method of fabricating a nanostructured tube of  claim 16 , wherein the reduction in the amount of force required allows continuation of cycles of extrusion without a need to constrain a sample length. 
     
     
       18. The method of fabricating a nanostructured tube of  claim 12 , wherein, during extrusion cycles, an amount of strain is applied on the sample billet, and the amount of strain deforms the sample billet to generate an ultrafine grained nanostructure for the sample billet. 
     
     
       19. The method of fabricating a nanostructured tube of  claim 18 , wherein a total amount of strain applied on the sample billet is equal to a summation of the amount of strain applied in each of the extrusion cycles. 
     
     
       20. The method of fabricating a nanostructured tube of  claim 18 , wherein the ultrafine grained nanostructure of the sample billet increases a mechanical strength of the sample billet.